Heart rhythm disorders are of great clinical significance. Imaging of cardiac electrical activity has important value in the investigation of underlying mechanisms of cardiac arrhythmias and their treatment, including interventional and surgical approaches. At the same time, imaging of electrical activity of the heart is challenging because cardiac electrical activity is time dependent and spatially distributed throughout the myocardium.
Conventional electrocardiographic methods, such as conventional 12-lead ECG, vectorcardiography and multichannel body surface ECG mapping techniques can be limited in their ability to provide information regarding regional electrical activity in the myocardium. Recording of local electrograms (EGs) on the epicardial and endocardial surfaces of the heart utilizing specialized recording devices such as intracardiac catheters or numerical reconstruction of the local EGs using body surface mapping data can provide more accurate cardiac electrical activity data.
Cardiac imaging using local electrograms suffers from several disadvantages, however. It is well known that local electrograms have two components—the “near field” reflecting local electrical activity of the myocardium, and the “far field” reflecting electrical activity of the entire myocardium. The presence of the far field component in electrograms complicates electrophysiological analysis, as electrograms do not show directly moments of activation and recovery of the myocardium. To map activation, common approaches include the use of empirical algorithms for electrogram processing (such as −du/dt max). However, such methods are typically not suitable for mapping reentrant arrhythmias (such as atrial and ventricular fibrillation, or polymorphic ventricular tachycardia) because local electrograms are often fractionated. Even greater difficulties can arise in detecting repolarization sequences of the myocardium.
Unlike electrograms, action potentials are signals that reflect intracellular myocardial electrical activity. Action potential signals, if they can be obtained or derived, permit activation and recovery times to be determined. Moreover, action potential signals (or “action potentials”) directly reflect cellular ionic currents. Consequently, action potentials permit the locations of cellular substrate of cardiac arrhythmias to be determined. Unfortunately, acquisition and/or derivation of action potential signals has proven to be notoriously difficult.
What is needed are improved methods and means of determining action potentials.